1. Field of the Invention
The present invention relates generally to gas turbine engines and, more particularly, to a tube coupling assembly for use in connecting fluid tubing of gas turbine engines.
2. Related Art
Gas turbine engines such as those used for aircraft propulsion necessarily include external tubing systems for delivering fluids, either gases or liquids, from one engine component to another or for connecting an engine component with an aircraft system. These tubing systems may include tube coupling assemblies, of various types, to connect adjacent fluid-carrying tubes or to connect a tube to another engine component.
One prior tube coupling assembly which has been used in gas turbine engine tubing systems is the B-nut, or ballnose fitting, assembly which comprises a tube connector having a first end operably affixable to a first fluid-carrying tube, a ferrule having a first end operably affixable to a second fluid-carrying tube, and a coupling nut having internal threads which engage external threads of the tube connector so as to urge the second ends of the tube connector and ferrule against one another in sealing engagement. Although the B-nut assembly has been advantageously used in a variety of gas turbine engine applications, it is subject to certain limitations. Since the tube connector may not rotate due to a fixed attachment to a fluid-carrying tube, the assembler is not forced to use a pair of wrenches to tighten the fittings. Instead, the assembly fittings may be tightened by using a single wrench to apply a torque to the wrenching surface of the rotatable coupling nut. If a second wrench is not used to apply a counter torque to the wrenching surface of the tube connector a torsional load is imposed on the fluid-carrying tube to which the tube connector is attached. This torsional load may result in failure of the fluid-carrying tube. Additionally, current B-nut assemblies have no means for accommodating angular misalignment between the fluid-carrying tubes being connected. If the tubes are forced into alignment at assembly a resultant bending load is reacted by the tubes which may lead to tube distress.
The coupling nut of the B-nut assembly typically includes drilled holes for allowing the nut to be safety-wired to another engine component to prevent loosening of the assembly fittings, i.e., to prevent the coupling nut from backing off of the tube connector by an amount which eliminates the tube connector/ferrule contact seal. However, the safety wires is difficult to install and if installed incorrectly can actually facilitate loosening of the assembly fittings so as to eliminate the contact seal.
Other tube fitting or coupling assemblies are known which include self locking features. An example of such an assembly is illustrated in U.S. Pat. No. 5,263,312 to Walker, et al. entitled "Tube Fitting For A Gas Turbine Engine," issued Nov. 23, 1993 and assigned to the assignee of the present invention, which illustrates a plurality of resilient figures 71 which engage a plurality of slots 63 in the outer circumferential surface 65 of B-nut 19. While the aforementioned locking feature scheme employing fingers 71 and slots 63 avoids the potential problems associated with safety-wiring the B-nut, and may be advantageously utilized, the external nature of the locking feature causes it to be susceptible to handling and operational damage. Another fitting assembly is known which also uses externally configured fingers and slots with the number of fingers being different than the number of slots, wherein this difference may be used to control the allowable rotational slip of the assembly between possible locked conditions. Other self-locking tube coupling assemblies are known which require additional parts such as springs or sawtooth washers wherein these parts increase assembly cost and decrease assembly reliability.
In view of the foregoing, prior to the present invention a need existed for an improved tube coupling assembly for use in fluid tubing systems to resolve the aforementioned problems associated with prior coupling, or fitting, assemblies.